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Model

Claude Sonnet 4.5

Claude Sonnet 4.5, released on 29 September 2025, was a drop-in replacement for Sonnet 4 at the same price. Anthropic reported that it could stay focused on complex tasks for more than 30 hours.

Status DeprecatedModality Text, ImageContext (K tokens) 200 Era Generative AI for everyone

License
Proprietary
Access
API, App, Enterprise
Release date
Developer
Anthropic

What it is

Claude Sonnet 4.5 is a large language model developed by Anthropic and released on 29 September 2025 under the API identifier claude-sonnet-4-5, with the snapshot claude-sonnet-4-5-20250929. It was positioned as a drop-in replacement for Sonnet 4, which means existing applications could switch to it without changing how they call the model. Its price matched Sonnet 4 at $3 per million input tokens and $15 per million output tokens.[1][2]

Origins

Claude Sonnet 4.5 followed Claude Sonnet 4, which was announced in May 2025. The launch was part of a wider set of tools for building with Claude. It came with the Claude Agent SDK, Claude Code checkpoints and a native VS Code extension, the API's context editing and memory tool, and code execution and file creation in the Claude apps.[1]

According to Wikipedia, its training data ran to July 2025.[3]

Main features

On SWE-bench Verified, a coding benchmark, the model scored 77.2%, an average over 10 trials with a 200K-token thinking budget. In a 1M-token context configuration it scored 78.2%, and with high compute it reached 82.0%.[1]

On OSWorld, a benchmark of computer use, in which a model operates a computer interface, it scored 61.4%. Sonnet 4 had scored 42.2% on the same benchmark about four months earlier.[1]

Anthropic observed the model maintaining focus for more than 30 hours on complex, multi-step tasks.[1]

Anthropic called it its “most aligned frontier model” so far. It showed reduced sycophancy, which means telling users what they want to hear, along with reduced deception, reduced power-seeking and less encouragement of delusional thinking. It also had stronger defences against prompt injection, in which hidden instructions in content try to hijack a model.[1]

The model was released under AI Safety Level 3 (ASL-3) protections. Classifier false positives, meaning harmless requests wrongly flagged, had fallen tenfold since they were first described. Its system card was the first to include tests using mechanistic interpretability techniques, which examine the internal computations of a model.[1]

Its place in development

Claude Sonnet 4.6 succeeded the model on 17 February 2026.[3]

Anthropic announced the model's deprecation on 30 September 2026. Retirement from the Claude API is scheduled for 30 November 2026.[2]

CapabilitiesLarge language modelsCodeAgents & tool use

Governance & standardsSafety & governance

Version history

20
  1. 2023
    • Mar 14, 2023 Claude (March 2023)

      Claude is the AI assistant Anthropic announced on 14 March 2023, its first publicly available assistant. It was built around training AI to be helpful, honest and harmless, and it started the Claude model line.

    • Jul 11, 2023 Claude 2

      Claude 2 is the second major version of Anthropic's assistant model, released on 11 July 2023 with better performance and longer responses. It was the first Claude model open to the general public.

    • Nov 21, 2023 Claude 2.1

      Claude 2.1, released on 21 November 2023, doubled the context window to 200,000 tokens and cut false statements by half compared with Claude 2.0. It added tool use and system prompts.

  2. 2024
    • Mar 4, 2024 Claude 3 Opus

      Claude 3 Opus, announced on 4 March 2024, was the most capable model in the Claude 3 family. It added vision and launched with a 200K-token context window and a Needle In A Haystack recall above 99%.

    • Mar 4, 2024 Claude 3 Sonnet

      Claude 3 Sonnet was the middle model of Anthropic's Claude 3 family, announced on 4 March 2024. It powered the free tier of claude.ai, offered a 200K-token context window, and was retired on 21 July 2025.

    • Jun 20, 2024 Claude 3.5 Sonnet

      Claude 3.5 Sonnet, released on 20 June 2024, was the first model of the Claude 3.5 family. It ran twice as fast as Claude 3 Opus at the mid-tier price and powered the new Artifacts and Projects features.

    • Oct 22, 2024 Claude 3.5 Sonnet (October 2024 upgrade)

      The upgraded Claude 3.5 Sonnet, announced on 22 October 2024, raised coding and agentic scores and introduced computer use in public beta, the first such offer from a frontier AI model.

  3. 2025
    • Feb 24, 2025 Claude 3.7 Sonnet

      Claude 3.7 Sonnet, released on 24 February 2025, was described by Anthropic as the first hybrid reasoning model on the market, able to answer quickly or think step by step at length. It launched with Claude Code.

    • May 22, 2025 Claude 4 (Claude Opus 4 and Claude Sonnet 4)

      Claude Opus 4 and Claude Sonnet 4, announced on 22 May 2025, were hybrid models with extended thinking. Anthropic called Opus 4 the best coding model in the world, and Claude Code became generally available the same day.

    • Aug 5, 2025 Claude Opus 4.1

      Claude Opus 4.1, released on 5 August 2025, upgraded Claude Opus 4 for agentic tasks, real-world coding and reasoning, at the same price. Anthropic later succeeded it with Claude Opus 4.5.

    • Sep 29, 2025 Claude Sonnet 4.5 · This page

      Claude Sonnet 4.5, released on 29 September 2025, was a drop-in replacement for Sonnet 4 at the same price. Anthropic reported that it could stay focused on complex tasks for more than 30 hours.

    • Nov 24, 2025 Claude Opus 4.5

      Claude Opus 4.5, released on 24 November 2025, cost a third as much as Opus 4.1 per token and introduced an effort parameter that lets developers trade capability for time and cost. Claude Opus 4.6 succeeded it.

  4. 2026
    • Feb 5, 2026 Claude Opus 4.6

      Released on 5 February 2026, Claude Opus 4.6 was an upgrade to Anthropic's smartest model. It was the first Opus-class model with a 1M-token context window, in beta at launch, and it introduced agent teams in Claude Code.

    • Feb 17, 2026 Claude Sonnet 4.6

      Released on 17 February 2026 with a 1M-token context window in beta, Claude Sonnet 4.6 kept the price of Sonnet 4.5 and became the default model for Free and Pro users on claude.ai.

    • Apr 16, 2026 Claude Opus 4.7

      Released on 16 April 2026 at the same price as Opus 4.6, Claude Opus 4.7 added an xhigh effort level and accepted much larger images. It was the first model to test automatic blocking of high-risk cybersecurity requests.

    • May 28, 2026 Claude Opus 4.8

      Released on 28 May 2026 at the same price as Opus 4.7, Claude Opus 4.8 added a fast mode at 2.5 times the speed, with fewer unnoticed flaws in its own code. Anthropic called it a modest but tangible improvement.

    • Jun 30, 2026 Claude Sonnet 5

      Claude Sonnet 5, released on 30 June 2026, is Anthropic's most agentic Sonnet model. It can make plans, use browsers and terminals, and run autonomously, at an introductory price of $2 and $10 per million tokens.

    • Jul 24, 2026 Claude Opus 5

      Claude Opus 5, released on 24 July 2026 at $5 and $25 per million tokens, is Anthropic's most aligned model to date and its most capable generally available model for scientific research.

    • Sep 22, 2026 Claude Opus 5.5

      Claude Opus 5.5, released on 22 September 2026, is the first model in Anthropic's Claude 5.5 family. Anthropic said it performs at the level of Fable 5.1 on most work, at about 40% lower cost than Opus 5.

    • Sep 28, 2026 Claude Sonnet 5.5

      Claude Sonnet 5.5, released on 28 September 2026, is the second model in the Claude 5.5 family and Anthropic's fastest Sonnet to date. It costs $2 and $10 per million tokens, with cache reads halved in October 2026.

20251

  1. ReleaseAnthropic releases Claude Sonnet 4.5 and the Claude Agent SDK

    On 29 September 2025 Anthropic released Claude Sonnet 4.5 at the same price as Sonnet 4, alongside the Claude Agent SDK, the toolkit behind Claude Code offered to other developers.

Developed by1

Anthropic

Successor of1

Claude 4 (Claude Opus 4 and Claude Sonnet 4)

Succeeded by1

Claude Sonnet 4.6

Powers3

Claude apps (claude.ai)Claude CodeClaude in Chrome

Uses3

TransformerChain of thought and reasoning modelsConstitutional AI

Notes and sources

  1. Introducing Claude Sonnet 4.5https://www.anthropic.com/news/claude-sonnet-4-5
  2. Model deprecationshttps://platform.claude.com/docs/en/about-claude/model-deprecations
  3. Claude (language model)https://en.wikipedia.org/wiki/Claude_(language_model)

Cite this page: Claude Sonnet 4.5. TellWorld, https://www.tellworld.net/models/claude-sonnet-4-5. Updated 2026-11-08